The administration of Richard Nixon feared that Israel may have been developing nuclear weapons as early as the 1960s according to newly released documents.

A memorandum from the former US president's then national security adviser, Henry Kissinger, in 1969 warned that "Israel's secret possession of nuclear weapons would increase potential danger in the Middle East".

However Kissinger, said: "I do not believe we can ask Israel not to produce missiles. Israel is sovereign in this decision."

The declassified memo, titled Israeli Nuclear Programme, released by the Nixon presidential library on Wednesday also indicated a desire to keep the alleged programme secret for fear of a nuclear arms race.

"In this case, public knowledge is almost as dangerous as possession itself," the memorandum, dated July 19 1969, said.

"What this means is that, while we might ideally like to halt actual Israeli possession, what we really want, at a minimum, may be just to keep Israeli possession from becoming an established international fact."

Israel has never confirmed publicly that it has a nuclear arms programme, maintaining what it calls a policy of "ambiguity" on the subject.

The memorandum from Kissinger came just a year after the Nuclear Non Proliferation Treaty (NPT) was opened for signature.

There are currently 189 countries signed up to the NPT and of the four non-signatories three are close US allies - India, Pakistan and Israel.

Missile concern

Kissinger indicates that "as a minimum, we want Israel to sign the NPT".

"This is not because signing will make any difference in Israel's actual nuclear programme because Israel could make weapons clandestinely."

The memorandum was issued over concern that Israel had 12 surface-to-surface missiles delivered from France and planned to have 10 nuclear warheads by the end of 1970 and was scheduled to receive Phantom aeroplanes from the US.

Coming just two years after Israel's war with its Arab neighbours in 1967, Kissinger said: "The Israelis, who are one of the few peoples whose survival is genuinely threatened, are probably more likely than almost any other to actually use their weapons."

He said there were fears Yitzhak Rabin, a future Israeli prime minister and then the ambassador to the US, would "stonewall" the administration over the issue.

Client privilege

"Our problem is that Israel will not take us seriously on the nuclear issue unless they believe we are prepared to withhold something they very much need - the Phantoms or, even more, their whole military supply relationship with us."

Marwan Bishara, Al Jazeera's senior political analyst, said there was an understanding at the time that the US would defend and perhaps "cover up" because Israel was a Cold war "client" against Soviet clients in the Middle East.

"That then became a problem because there was a real threat of Israel using those weapons in 1967 or later 1973 because Israel actually assembled these weapons during those wars," he said.

Bishara said the memorandum has a relevance to current US opposition to any nuclear programme in Iran.

"As the US discusses the Iranian threat of perhaps delivering nuclear weapons, Israel is on the record as having a nuclear bomb," he said.

Kissinger's memorandum is part of a series of previously classified documents from the Nixon presidential library released by the US national archives under an order whereby documents are reviewed and declassified after 25 years.